“There was nothing there but rubble, “Mike said. “We’re talking about a 50 ton hydraulic press – gone!” The two began yelling for their co-workers, but there was no answer. They saw a perfect line of smoke streaming through the air. “You could stand here,” he said, “and two inches over you couldn’t breathe. We couldn’t see through the smoke so we started screaming.” But there was still no answer.

The two made their way to the parking garage, but found that it, too, was gone. “There were no walls, there was rubble on the floor, and you can’t see anything” he said.

They decided to ascend two more levels to the building’s lobby. As they ascended to the B Level, one floor above, they were astonished to see a steel and concrete fire door that weighed about 300 pounds, wrinkled up “like a piece of aluminum foil” and lying on the floor. “They got us again,” Mike told his co-worker, referring to the terrorist attack at the center in 1993. Having been through that bombing, Mike recalled seeing similar things happen to the building’s structure. He was convinced a bomb had gone off in the building."

http://search.barnesandnoble.com/booksearch/isbninquiry.asp?ean=9780452283954&displayonly=EXC
Will Jimeno; PAPD: Our inspector commandeered a bus, and we sped down—the sector cars opened the way for us. We go to the north tower, and then we go under the buildings to go to the south tower, to get to the lobby there. We are one floor under the main concourse area, where all the stores are, and pushing a cart filled with equipment, air masks, helmets, axes, tools, and so on. On the back of the cart, pushing, is Antonio Rodrigues, and just to his left is Christopher Amoroso. [Suddenly I hear a loud noise and] look over to the sarge and say, "Hey, Sarge, is there a second plane coming?" And, just then, it is like an earthquake when the plane hits the south building. We are just about in the middle of the concourse, between the two buildings, just below and a little south of the big golden globe, when huge parts of the tower and shock waves come down into the plaza area, cracking all the cement. The whole concourse above us collapses. There are a lot of civilians all around, and I don't know what happens to them, but I think it has to be bad. I can see Liberty Street before me as I feel a ball of debris hit us. Now, I see a huge fireball coming at us, and I yell, "Run! Run towards the freight elevator!"

Dominick runs first, I am behind, and the sarge is behind me. Antonio is behind the sarge, and Chris is bringing up the rear. But Chris never makes it because the shock wave pushes him back into the main concourse area, and he takes the worst of it. Dominick and I and the sarge just make it around the corner, but Antonio doesn't. Everything just starts hitting us, and then the wall comes down on top of me. I am flabbergasted. My friend Dominick is crushed down in the push-up position, and my legs are pinned completely by heavy concrete. Sergeant McLoughlin sees the walls breaking apart, and they are falling on him. And the ceiling falls on him, [pinning him] twenty feet away from me. I can't see him, but I can hear him. I keep calling out for Amoroso and Rodrigues, calling and calling for two minutes straight. But there is no response.

Steve Evans; BBC reporter: "I was at the base of the 2nd tower, the second tower that was hit. There was an explosion - I didn't think it was an explosion - but the base of the building shook. I felt it shake - then when we were outside, the second explosion happened and then there was a series of explosions. We can only wonder at the kind of damage -- the kind of human damage -- which was caused by those explosions - those series of explosions."

Steve Evans; BBC reporter: "There were two or three similar huge explosions and the building literally shook."

http://www.thememoryhole.org/911/veliz-bombs.htm
Teresa Veliz, the facilities manager for a software development company, was on the 47th floor of the North Tower when Flight 11 hit. First, like many witnesses, she describes the building shaking twice:"I got off [the elevator], turned the corner and opened the door to the ladies' room. I said good morning to a lady sitting at a mirror when the whole building shook. I thought it was an earthquake. Then I heard those banging noises on the other side of the wall. It sounded like someone had cut the elevator cables. It just fell and fell and fell.

I began to cry. "Oh, my God, I just got off that elevator!" I said. "That could have been me." I prayed those other people had gotten off on the 48th floor before the elevator dropped. But I didn't have much time to be upset because the building shook again, this time even more violently. The lady at the mirror grabbed onto me and held on for dear life."
[...]